If a Grover is by himself, this can give any champion with decent mobility a chance to close the distance between them and Grover. The closer you get, the more damage you do and the less damage Grover does. Don’t forget about the vine though!
His insta heal is big, but only when ally is in his circle. Firstly you and "your allies" should pay attention to "his allies" and them occupy with something. Then when Grover is left alone it's your chance to challenge him on solo fight.
Try to take out ling range targets like kinessa. And try to predict the position of fast moving champions.
Be the last one down by timing your heals so that your team can regroup around you even if you die by then
Unlike most front liners and supports grover has very good long range pressure. He can use his bonus damage scaling legendary to harass enemy front liners from long range or long range enemies from the objective easily.